Relay backhaul uplink HARQ protocol

ABSTRACT

The present invention relates to a method for configuring a retransmission protocol on the uplink between a network node and a relay node in a mobile communication system, the configuration being performed at a network node or at a relay node, and to the corresponding relay node apparatus and network node apparatus capable of configuring the retransmission protocol. In particular, the number of transmission processes is determined based on the position of time intervals available for the transmission and may be selected in order to control the round trip time of the retransmission protocol. Once the number of transmission processes has been configured, the transmission processes are mapped on the available time intervals in a predefined order and repetitively.

The present invention relates to a retransmission protocol for a mobilecommunication system.

BACKGROUND OF THE INVENTION

Third-Generation (3G) mobile systems, such as for instance UniversalMobile Telecommunications System (UMTS) standardized within theThird-Generation Partnership Project (3GPP), have been based on WidebandCode Division Multiple Access (WCDMA) radio access technology. Today,the 3G systems are being deployed on a broad scale all around the world.After enhancing this technology by introducing High-Speed DownlinkPacket Access (HSDPA) and an enhanced uplink, the next major step inevolution of the UMTS standard has brought a combination of OrthogonalFrequency Division Multiplexing (OFDM) for the downlink and SingleCarrier Frequency Division Multiplexing Access (SC-FDMA) for the uplink.This system has been named Long-Term Evolution (LTE) since it has beenintended to cope with future technology evolutions.

The target of LTE is to achieve significantly higher data rates comparedto HSDPA and HSUPA, to improve the coverage for the high data rates, tosignificantly reduce latency in the user plane in order to improve theperformance of higher layer protocols (for example, TCP), as well as toreduce delay associated with control plane procedures such as, forinstance, session setup. Focus has been given to the convergence towardsuse of Internet Protocol (IP) as a basis for all future services, and,consequently, on the enhancements to the packet-switched (PS) domain.LTE's radio access shall be extremely flexible, using a number ofdefined channel bandwidths between 1.25 and 20 MHz (contrasted withoriginal UMTS fixed 5 MHz channels).

A radio access network is responsible for handling all radio-accessrelated functionality including scheduling of radio channel resources.The core network may be responsible for routing calls and dataconnections to external networks. In general, today's mobilecommunication systems (for instance GSM, UMTS, cdma200, IS-95, and theirevolved versions) use time and/or frequency and/or codes and/or antennaradiation pattern to define physical resources. These resources can beallocated for a transmission for either a single user or divided to aplurality of users. For instance, the transmission time can besubdivided into time periods usually called time slots then may beassigned to different users or for a transmission of data of a singleuser. The frequency band of such a mobile systems may be subdivided intomultiple subbands. The data may be spread using a (quasi) orthogonalspreading code, wherein different data spread by different codes may betransmitted using, for instance, the same frequency and/or time. Anotherpossibility is to use different radiation patterns of the transmittingantenna in order to form beams for transmission of different data on thesame frequency, at the same time and/or using the same code.

FIG. 1 schematically illustrates LTE architecture. The LTE network is atwo-node architecture consisting of access gateways (aGW) 110 andenhanced network nodes, so-called eNode Bs (eNB) 121, 122 and 123. Theaccess gateways handle core network functions, i.e. routing calls anddata connections to external networks, and also implement radio accessnetwork functions. Thus, the access gateway may be considered ascombining the functions performed by Gateway GPRS Support Node (GGSN)and Serving GPRS Support Node (SGSN) in today's 3G networks and radioaccess network functions, such as for example header compression,ciphering/integrity protection. The eNodeBs handle functions such as forexample Radio Resource Control (RRC), segmentation/concatenation,scheduling and allocation of resources, multiplexing and physical layerfunctions. The air (radio) interface is thus an interface between a UserEquipment (UE) and an eNodeB. Here, the user equipment may be, forinstance, a mobile terminal 132, a PDA 131, a portable PC, a PC, or anyother apparatus with receiver/transmitter conform to the LTE standard.

Multi carrier transmission introduced on the enhanced UMTS terrestrialradio access network (E-UTRAN) air interface increases the overalltransmission bandwidth, without suffering from increased signalcorruption due to radio-channel frequency selectivity. The proposedE-UTRAN system uses OFDM for the downlink and SC-FDMA for the uplink andemploys MIMO with up to four antennas per station. Instead oftransmitting a single wideband signal such as in earlier UMTS releases,multiple narrow-band signals referred to as “subcarriers” are frequencymultiplexed and jointly transmitted over the radio link. This enablesE-UTRA to be much more flexible and efficient with respect to spectrumutilization.

FIG. 2 illustrates an example of E-UTRAN architecture. The eNBscommunicate with the Mobility Management Entity (MME) and/or servinggateway (S-GW) via an interface S1. Furthermore, eNBs communicate witheach other over an interface X2.

In order to suit as many frequency band allocation arrangements aspossible, LTE standard supports two different radio frame structures,which are applicable to Frequency Division Duplex (FDD) and TimeDivision Duplex (TDD) modi of the standard. LTE can co-exist withearlier 3GPP radio technologies, even in adjacent channels, and callscan be handed over to and from all 3GPP's previous radio accesstechnologies.

The general baseband signal processing in LTE downlink is shown in FIG.3 (cf. 3GPP TS 36.212 “Multiplexing and Channel Coding”, Release 8, v.8.3.0, May 2008, available at http://www.3gpp.org and incorporatedherein by reference). First, information bits, which contain the userdata or the control data, are block-wise encoded (channel coding by aforward error correction such as turbo coding) resulting in codewords.The blocks of encoded bits (codewords) are then scrambled 310. Byapplying different scrambling sequences for neighbouring cells indownlink, the interfering signals are randomized, ensuring fullutilisation of the processing gain provided by the channel code. Theblocks of scrambled bits (codewords), which form symbols of predefinednumber of bits depending on the modulation scheme employed, aretransformed 320 to blocks of complex modulation symbols using the datamodulator. The set of modulation schemes supported by LTE downlink (DL)includes QPSK, 16-QAM and 64-QAM corresponding to two, four or six bitsper modulation symbol.

Layer mapping 330 and precoding 340 are related toMultiple-Input/Multiple-Output (MIMO) applications supporting morereceiving and/or transmitting antennas. The complex-valued modulationsymbols for each of the codewords to be transmitted are mapped onto oneor several layers. LTE supports up to four transmitting antennas. Theantenna mapping can be configured in different ways to provide multiantenna schemes including transmit diversity, beam forming, and spatialmultiplexing. The set of resulting symbols to be transmitted on eachantenna is further mapped 350 on the resources of the radio channel,i.e., into the set of resource blocks assigned for particular UE by ascheduler for transmission. The selection of the set of resource blocksby the scheduler depends on the channel quality indicator (CQI)—feedbackinformation signalized in the uplink by the UE and reflecting themeasured channel quality in the downlink. After mapping of symbols intothe set of physical resource blocks, an OFDM signal is generated 360 andtransmitted from the antenna ports. The generation of OFDM signal isperformed using inverse discrete Fourier transformation (fast Fouriertransformation FFT).

The LTE uplink transmission scheme for both FDD and TDD mode is based onSC-FDMA (Single Carrier Frequency Division Multiple Access) with cyclicprefix. A DFT-spread-OFDM method is used to generate an SC-FDMA signalfor E-UTRAN, DFT standing for Discrete Fourier Transformation. ForDFT-spread-OFDM, a DFT of size M is first applied to a block of Mmodulation symbols. The E-UTRAN uplink supports, similarly to thedownlink QPSK, 16-QAM and 64-QAM modulation schemes. The DFT transformsthe modulation symbols into the frequency domain and the result ismapped onto consecutive subcarriers. Subsequently, an inverse FFT isperformed is performed as in OFDM downlink, followed by addition of thecyclic prefix. Thus, the main difference between SC-FDMA and OFDMAsignal generation is the DFT processing. In an SC-FDMA signal, eachsubcarrier contains information of all transmitted modulation symbols,since the input data stream has been spread by the DFT transform overthe available subcarriers. In OFDMA signal, each subcarrier only carriesinformation related to specific modulation symbols. The uplink (UL) willsupport BPSK, QPSK, 8PSK and 16QAM.

FIG. 4 illustrates the time domain structure for LTE transmissionapplicable to FDD mode. The radio frame 430 has a length of T_(frame)=10ms, corresponding to the length of a radio frame in previous UMTSreleases. Each radio frame further consists of ten equally sizedsubframes 420 of the equal length T_(subframe)=1 ms. Each subframe 420further consists of two equally sized time slots (TS) 410 of lengthT_(slot)=0.5 ms. Up to two codewords can be transmitted in one subframe.

FIG. 5 illustrates the time domain structure for LTE transmissionapplicable to TDD mode. Each radio frame 530 of length T_(frame)=10 msconsists of two half-frames 540 of length 5 ms each. Each half-frame 540consists of five subframes 520 with length T_(subframe)=1 ms and eachsubframe 520 further consists of two equally sized time slots 510 oflength T_(slot)=0.5 ms.

Three special fields called DwPTS 550, GP 560, and UpPTS 570 areincluded in each half-frame 540 in subframe number SF1 and SF6,respectively (assuming numbering of ten subframes within a radio framefrom SF0 to SF9). Subframes SF0 and SF5 and special field DwPTS 350 arealways reserved for downlink transmission.

The physical resources for the OFDM (DL) and SC-FDMA (UL) transmissionare often illustrated in a time-frequency grid wherein each columncorresponds to one OFDM or SC-FDMA symbol and each row corresponds toone OFDM or SC-FDMA subcarrier, the numbering of columns thus specifyingthe position of resources within the time domain, and the numbering ofthe rows specifying the position of resources within the frequencydomain.

The time-frequency grid of N_(RB) ^(UL)N_(sc) ^(RB) subcarriers andN_(symb) ^(UL) SC-FDMA symbols for a time slot TSO 610 in uplink isillustrated in FIG. 6. The quantity N_(RB) ^(UL) depends on the uplinktransmission bandwidth configured in the cell. The number N_(symb) ^(UL)of SC-FDMA symbols in a time slot depends on the cyclic prefix lengthconfigured by higher layers. A smallest time-frequency resourcecorresponding to a single subcarrier of an SC-FDMA symbol is referred toas a resource element 620. A resource element 620 is uniquely defined bythe index pair (k,l) in a time slot where k=0, . . . , N_(RB)^(UL)N_(sc) ^(RB)−1 and l=0, . . . , N_(symb) ^(UL)−1 are the indices inthe frequency and time domain, respectively. The uplink subcarriers arefurther grouped into resource blocks (RB) 630. A physical resource blockis defined as N_(symb) ^(UL) consecutive SC-FDMA symbols in the timedomain and N_(sc) ^(RB) consecutive subcarriers in the frequency domain.Each resource block 630 consists of twelve consecutive subcarriers andspan over the 0.5 ms slot 610 with the specified number of SC-FDMAsymbols.

In 3GPP LTE, the following downlink physical channels are defined (3GPPTS 36.211 “Physical Channels and Modulations”, Release 8, v. 8.3.0, May2008, available at http://www.3gpp.org):

-   -   Physical Downlink Shared Channel (PDSCH)    -   Physical Downlink Control Channel (PDCCH)    -   Physical Broadcast Channel (PBCH)    -   Physical Multicast Channel (PMCH)    -   Physical Control Format Indicator Channel (PCFICH)    -   Physical HARQ Indicator Channel (PHICH)

In addition, the following uplink channels are defined:

-   -   Physical Uplink Shared Channel (PUSCH)    -   Physical Uplink Control Channel (PUCCH)    -   Physical Random Access Channel (PRACH).

The PDSCH and the PUSCH are utilized for data and multimedia transportin downlink (DL) and uplink (UL), respectively, and hence designed forhigh data rates. The PDSCH is designed for the downlink transport, i.e.from eNode B to at least one UE. In general, this physical channel isseparated into discrete physical resource blocks and may be shared by aplurality of UEs. The scheduler in eNodeB is responsible for allocationof the corresponding resources, the allocation information issignalized. The PDCCH conveys the UE specific and common controlinformation for downlink and the PUCCH conveys the UE specific controlinformation for uplink transmission.

Downlink control signalling is carried by the following three physicalchannels:

-   -   Physical Control Format Indicator Channel (PCFICH) utilized to        indicate the number of OFDM symbols used for control channels in        a subframe,    -   Physical Hybrid Automatic Repeat Request Indicator Channel        (PHICH) utilized to carry downlink acknowledgements (positive:        ACK, negative: NAK) associated with uplink data transmission,        and    -   Physical Downlink Control Channel (PDCCH) which carries downlink        scheduling assignments and uplink scheduling grants.

In LTE, the PDCCH is mapped to the first n OFDM symbols of a subframe,wherein n is more than or equal to 1 and is less than or equal to three.Transmitting PDCCH in the beginning of the subframe has the advantage ofearly decoding of the corresponding L1/L2 control information includedtherein.

Hybrid ARQ is a combination of Forward Error Correction (FEC) and theretransmission mechanism Automatic Repeat reQuest (ARQ). If a FECencoded packet is transmitted and the receiver fails to decode thepacket correctly, the receiver requests a retransmission of the packet.Errors are usually checked by a CRC (Cyclic Redundancy Check) or byparity check code. Generally, the transmission of additional informationis called “retransmission (of a data packet)”, although thisretransmission does not necessarily mean a transmission of the sameencoded information, but could also mean the transmission of anyinformation belonging to the packet (e.g. additional redundancyinformation).

In LTE there are two levels of re-transmissions for providingreliability, namely, HARQ at the MAC (Medium Access Control) layer andouter ARQ at the RLC (Radio Link Control) layer. The outer ARQ isrequired to handle residual errors that are not corrected by HARQ thatis kept simple by the use of a single bit error-feedback mechanism, i.e.ACK/NACK.

On MAC, LTE employs a hybrid automatic repeat request (HARQ) as aretransmission protocol. The HARQ in LTE is an N-process Stop-And-Waitmethod HARQ with asynchronous re-transmissions in the downlink andsynchronous re-transmissions in the uplink. Synchronous HARQ means thatthe re-transmissions of HARQ blocks occur at predefined periodicintervals. Hence, no explicit signaling is required to indicate to thereceiver the retransmission schedule. Asynchronous HARQ offers theflexibility of scheduling re-transmissions based on air interfaceconditions. In this case an identification of the HARQ process needs tobe signaled in order to enable a correct combing and protocol operation.HARQ operation with eight processes is decided for LTE.

In uplink HARQ protocol operation there are two different options on howto schedule a retransmission. Retransmissions in a synchronousnon-adaptive retransmission scheme are either scheduled by a NAK.Retransmissions in a synchronous adaptive retransmissions mechanism areexplicitly scheduled on PDCCH.

In case of a synchronous non-adaptive retransmission the retransmissionwill use the same parameters as the previous uplink transmission, i.e.the retransmission will be signaled on the same physical channelresources respectively uses the same modulation scheme. Sincesynchronous adaptive retransmission is explicitly scheduled via PDCCH,the eNB has the possibility to change certain parameters for theretransmission. A retransmission could be for example scheduled on adifferent frequency resource in order to avoid fragmentation in theuplink, or the eNB could change the modulation scheme or alternativelyindicate to the UE what redundancy version to use for theretransmission. It should be noted that the HARQ feedback including apositive or a negative acknowledgement (ACK/NAK) and PDCCH signalingoccurs at the same timing. Therefore the UE only needs to check oncewhether a synchronous non-adaptive retransmission is triggered, whetheronly a NAK is received, or whether eNB requests a synchronous adaptiveretransmission, i.e. a PDCCH is signaled in addition to the HARQfeedback on PHICH. The maximum number of retransmissions is configuredper UE rather than per radio bearer.

The time schedule of the uplink HARQ protocol in LTE is illustrated inFIG. 7. The eNB transmits to the UE a first grant 701 on PDCCH. Inresponse to the first grant 701, the UE transmits first data 702 to theeNB on PUSH. The timing between PDCCH uplink grant and PUSCHtransmission is fixed to 4 ms. After receiving the first transmission702, from the UE, the eNB transmits a second grant or feedbackinformation (ACK/NAK) 703. The timing between the PUSCH transmission andthe corresponding PHICH carrying the feedback information is fixed to 4ms. Consequently, the Round Trip Time (RTT) indicating the next chanceof transmission in LTE Release 8 uplink HARQ protocol is 8 ms. Afterthese 8 ms, the UE may transmit a second data 704.

Measurement gaps for performing measurements at the UE are of higherpriority than HARQ retransmissions. Whenever an HARQ retransmissioncollides with a measurement gap, the HARQ retransmission does not takeplace.

A key new feature of LTE is the possibility to transmit multicast orbroadcast data from multiple cells over a synchronized single frequencynetwork. This feature is called Multimedia Broadcast Single FrequencyNetwork (MBSFN) operation. In MBSFN operation, UE receives and combinessynchronized signals from multiple cells. In order to enable MBSFNreception, a UE needs to perform a separate channel estimation based onMBSFN Reference Signal (MBSFN RS). In order to avoid mixing MBSFN RS andnormal reference signals in the same subframe, certain subframes knownas MBSFN subframe, are reserved for MBSFN transmission. In an MBSFNsubframe, up to two of the first OFDM symbols are reserved for anon-MBSFN transmission and the remaining OFDM symbols are used for MBSFNtransmission. In the first up to two OFDM symbols, signalling data iscarried such as PDCCH for transmitting uplink grants and PHICH fortransmitting ACK/NAK feedback. The cell specific reference signal is thesame as for non-MBSFN subframes.

The pattern of subframes reserved for MBSFN transmission in a cell isbroadcasted in the System Information of the cell. Subframes withnumbers 0, 4, 5 and 9 cannot be configured as MBSFN subframes. MBSFNsubframe configuration supports both 10 ms and 40 ms periodicity. Inorder to support the backward compatibility, the UEs, which are notcapable of receiving MBSFN, shall decode the first up to two OFDMsymbols and ignore the remaining OFDM symbols in the subframe.

The International Telecommunication Union (ITU) has coined the termInternational mobile Communication (IMT) Advanced to identify mobilesystems whose capabilities go beyond those of IMT-2000. In order to meetthis new challenge, 3GPPs organizational partners have agreed to widenthe scope of 3GPP study and work to include systems beyond 3G. Furtheradvances for E-UTRA (LTE-Advanced) should be studied in accordance withthe 3GPP operator requirements for the evolution of E-UTRA and with theneed to meet/exceed the IMT-Advanced capabilities. The Advanced E-UTRAis expected to provide substantially higher performance compared to theexpected IMT-Advanced requirements in ITU Radio.

In order to increase the overall coverage and the coverage for serviceswith high data rates, to improve group mobility, enable temporarynetwork deployment and increase thesell-edge throughput, relaying isstudied for LTE-Advanced. In particular, a relay node is wirelesslyconnected to the radio-access network via a so-called donor cell.Depending on the relaying strategy, the relay node may be a part of thedonor cell or may control its own cells. When the relay node (RN) ispart of a donor cell, the relay node does not have its own cell identitybut may still have a relay ID. At least part of the radio resourcemanagement (RRM) is controlled by the eNB to which the donor cellbelongs, while parts of the RRM may be located in the relay. In thiscase, a relay should preferably support also Rel-8 LTE UEs. Smartrepeaters, decode-and-forward relays and different types of Layer 2relays are examples of this type of relaying.

If the relay node is in control of cells of its own, the relay nodecontrols one or several cells and a unique physical-layer cell identityis provided in each of the cells controlled by the relay node. The sameRRM mechanisms are available and from a UE perspective there is nodifference in accessing cells controlled by a relay and cells controlledby a “normal” eNodeB. The cells controlled by the relay should supportalso Rel-8 LTE UEs. Self-backhauling (Layer 3 relay) uses this type ofrelaying.

The connection of the relay to the network may be an inband connection,in which the network-to-relay link shares the same band with directnetwork-to-UE links within the donor cell. Release 8 UEs should be ableto connect to the donor cell in this case. Alternatively, the connectionmay be an outband connection, in which the network-to-relay link doesnot operate in the same band as direct network-to-UE links within thedonor cell.

With respect to the knowledge in the UE, relays can be classified intotransparent, in which case the UE is not aware of whether or not itcommunicates with the network via the relay, and non-transparent, inwhich case the UE is aware of whether or not it is communicating withthe network via the relay.

At least so-called “Type 1” relay nodes are part of LTE-Advanced. A“type 1” relay node is a relay node characterized by the followingfeatures:

-   -   It controls cells, each of which appears to a UE as a separate        cell distinct from the donor cell.    -   The cells shall have its own physical cell ID (defined in LTE        Rel-8) and the relay node shall transmit its own synchronization        channels, reference symbols, etc.    -   In the context of a single-cell operation, the UE shall receive        scheduling information and HARQ feedback directly from the relay        node and send its control channels (SR/CQI/ACK) to the relay        node.    -   The relay node shall appear as a Rel-8 eNB to Rel-8 UEs, in        order to provide backward compatibility.    -   In order to allow for further performance enhancement, a type-1        relay node shall appear differently from the Rel-8 eNB to the        LTE-Advanced UEs.

The LTE-A network structure of an E-UTRAN with a donor eNB 810 in adonor cell 815 and a relay node 850 providing a relay cell 855 to a UE890 is shown in FIG. 8. The link between the donor eNB (d-eNB) 810 andthe relay node 850 is named as relay backhaul link. The link between therelay node 850 and the UEs (r-UEs) 890 attached to the relay node iscalled relay access link.

If the link between the d-eNB 810 and the relay node 850 operates on thesame frequency spectrum as the link between the relay node 850 and theUE 980, simultaneous transmissions on the same frequency resourcebetween the d-eNB 810 and the relay node 850, and between the relay node850 and the UE 890, may not be feasible since the relay node transmittercould cause interference to its own receiver unless sufficient isolationof the outgoing and incoming signals is provided. Therefore, when therelay node 850 transmits to the donor d-eNB 810, it cannot receive fromthe UEs 890 attached to the relay node. Similarly, when the relay node850 receives from the donor eNB 810, it cannot transmit to the UEs 890attached to the relay node.

Consequently, there is a subframe partitioning between the relaybackhaul link (link between the d-eNB and the relay node) and relayaccess link (link between the relay node and a UE). It has beencurrently agreed that relay backhaul downlink subframes, during which adownlink backhaul transmission (d-eNB to relay node) may occur, aresemi-statically assigned, for instance, configured by radio resourceprotocol (by d-eNB). Furthermore, relay backhaul uplink subframes,during which an uplink backhaul transmission may occur (relay node tod-eNB), are semi-statically assigned or implicitly derived by HARQtiming from the relay backhaul downlink subframes.

In the relay backhaul downlink subframes, the relay node 850 willtransmit to the d-eNB 810. Thus, the r-UEs 890 are not supposed toexpect any transmission from the relay node 850. In order to supportbackward compatibility for r-UEs 890, the relay node 850 configuresbackhaul downlink subframes as MBSFN subframes in the relay node 850.

FIG. 9 illustrates the structure of such a relay backhaul downlinktransmission. As shown in FIG. 3, each relay backhaul downlink subframeconsists of two parts, control symbols 911 and data symbols 915. In thefirst up to two OFDM symbols, the relay node transmits to the r-UEscontrol symbols as in case of a normal MBSFN subframe. In the remainingpart of the subframe, the relay node may receive data 931 from thed-eNB. Thus, there cannot be any transmission from the relay node to ther-UE in the same subframe 922. The r-UE receives the first up to twoOFDM control symbols and ignores the rest part 932 of the subframe 922marked as an MBSFN subframe. Non-MBSFN subframes 921 are transmittedfrom the relay node to the r-UE and the control symbols as well as thedata symbols 941 are processed by the r-UE.

An MBSFN subframe can be configured for every 10 ms or every 40 ms,thus, the relay backhaul downlink subframes also support both 10 ms and40 ms configuration. Similarly to the MBSFN subframe configuration, therelay backhaul downlink subframes cannot be configured at subframes withnumbers 0, 4, 5 and 9. Those subframes that are not allowed to beconfigured as backhaul downlink subframes are called “illegal DLsubframes” throughout this document.

FIG. 10 shows applying of the LTE release 8 uplink HARQ protocol on therelay backhaul link. If LTE Release 8 uplink HARQ protocol (cf. FIG. 7)is reused on the relay uplink backhaul link 1001 between a relay nodeand a d-eNB, then a PDCCH (for transmitting an uplink grant 1021) inrelay downlink backhaul subframe m is associated with a PUSCHtransmission 1022 in a relay uplink backhaul subframe m+4. The PUSCHtransmission in the relay uplink backhaul subframe m−4 is in turnassociated with a PDCCH/PHICH in a relay downlink backhaul subframe m+8.When PDCCH/PHICH subframe timing in relay downlink backhaul collideswith illegal downlink subframes 1010, PDCCH/PHICH cannot be received bythe relay node.

In order to handle the collocation of PDCCH/PHICH subframe in relaydownlink backhaul with the illegal downlink subframes 1010, an approachsimilar to Release 8 measurement gap procedure may be adopted. Such aprocedure is illustrated in FIG. 11.

In FIG. 11, subframes with number 0, 4, 5 and 9 are illegal downlinksubframes 1110, in which cannot be used as backhaul downlink 1101subframes. In subframe 1 an uplink grant is transmitted from the d-eNBto the relay node. The corresponding data should be sent on PUSH fromthe relay node to the d-eNB four subframes later. The next backhauldownlink transmission would be another four subframes later, i.e., inthe subframe number 9, which is an illegal downlink subframe. Thus, insubframe 1120 no feedback will be transported on PDCCH/PHICH. In orderto handle this situation, the missed PHICH 1120 is interpreted as apositive acknowledgement (ACK), which triggers the suspension of theassociated UL HARQ process. If necessary, an adaptive retransmission canbe triggered later using PDCCH 1130. However, as a consequence of themissed PHICH, the associated relay uplink HARQ process loses theopportunity to transmit on the relay backhaul uplink when collisionoccurs. Within 40 ms, for each relay uplink HARQ process two collisionsoccur, which means that two uplink transmission opportunities are lost.In Release 8 UL synchronous HARQ protocol, if one uplink transmissionopportunity is lost, the associated uplink HARQ process has to wait 8 msfor the next UL transmission opportunity. Thus, the Round Trip Time(RTT) 1140 is increased to 16 ms. This causes increase of the averageRTT on relay uplink backhaul from 8 ms (as in Release 8) to (8 ms+16ms+16 ms)/3=13.3 ms.

This problem with the increased round trip time may be solved bychanging the system round trip time from 8 ms in Release 8 to 10 ms.Accordingly, the d-eNB sends ACK/NAK feedback on PHICH to the relay node10 ms after the d-eNB sends the uplink grant to the relay node. Thissolution is illustrated in FIG. 12. An initial assignment (uplink grant)1201 is transmitted from the d-eNB to the relay node. In response to theinitial assignment 1201, four milliseconds later the relay nodetransmits data 1202 in its first transmission on PUSH to the d-eNB. Thed-eNB provides an ACK/NAK feedback 1203 on PHICH six milliseconds later,i.e. in the subframe number 13. Upon receiving the ACK/NAK feedback1203, the relay node may retransmit the data 1204 ten milliseconds afterthe first transmission. Thus, the round trip time 1210 of 10 ms is thenew system round trip time fixed by the prescribed timing. Since anMBSFN subframe can be configured every 10 ms, there would be nocollisions with the illegal downlink subframes and PDCCH/PHICH canalways be received. Moreover, the average round trip time is equal tothe system round trip time of 10 ms.

However, the solution described with reference to FIG. 12 also does notsupport the 40 ms periodicity of MBSFN configuration. This limits thescheduling of d-eNB and has also impact on the r-UEs.

SUMMARY OF THE INVENTION

The aim of the present invention is to overcome this problem and toprovide an efficient retransmission protocol for data transmissionbetween two nodes in a mobile communication system, the retransmissionprotocol having a possibly low average round trip time and a possiblysmall amount of required control signalling overhead.

This is achieved by the features of the independent claims.

Advantageous embodiments of the present invention are subject matter ofthe dependent claims.

It is the particular approach of the present invention to select thenumber of transmission processes for data transmission between two nodesin a mobile communication system based on the time intervals availablefor data transmission, and to map the transmission processes onto theavailable time intervals in a predefined order and periodically repeatedfashion.

Such a configuration enables, for instance, an employment of asynchronous retransmission protocol for the uplink transmission in arelay. Due to the synchronous mapping of the transmission processes, therequired control signaling overhead is kept low. Moreover, differentpatterns and timings of the time intervals available for transmission ofdata between the two nodes may be supported.

According to a first aspect of the present invention, a method for datatransmission from a first node to a second node in a mobilecommunication system is provided. The method comprises determiningpositions of time intervals available for data transmission from thefirst node to the second node, selecting a number of transmissionprocesses for transmitting data from the first node to the second nodebased on the determined positions of the available time intervals; andderiving the position of time intervals for transmitting the databelonging to the selected number of transmission process from the firstnode to the second node according to the position of the available timeintervals and according to a mapping of the selected number oftransmission processes onto the available time intervals in a predefinedorder in a cyclically repeating fashion, wherein a first transmissionand any required retransmission of a single data portion are mapped to asingle transmission process.

In particular, the retransmission protocol may be an uplinkretransmission protocol including transmission of an uplink grant fromthe second node to the first node. The reception of an uplink granttriggers transmission of the uplink data from the first node to thesecond node. Moreover, the uplink retransmission protocol may includetransmitting of feedback information such as a positive or a negativeacknowledgement from the second node to the first node. The transmissionof the uplink grant may be realized in the same time interval as thetransmission of the feedback information. The transmission data may beeither a data that is transmitted for the first time, or data that isretransmitted.

Preferably, the time intervals available for transmission of data fromthe first node to the second node are determined based on knowledge ofthe positions of the time intervals already reserved for transmission ofdata from the second node to the first node.

Preferably, the first node is a relay node and the second node is a(base station) network node. However, the present invention may be usedfor communication between any two nodes in a mobile communicationsystem. For instance, the retransmission protocol may be used forcommunication between a terminal and a network node, or betweenarbitrary network nodes.

According to another aspect of the present invention, a data receivingnode communicating with a data transmitting node in a mobilecommunication system using a retransmission protocol for datatransmission from a data transmitting node to the data receiving node isprovided. The data receiving node comprises a link control unit fordetermining position of time intervals available for data transmissionfrom the data transmitting node to the data receiving node; atransmission control unit for choosing a number of transmissionprocesses for transmitting data from the data transmitting node to thedata receiving node based on the position of the available timeintervals determined by the link control unit. The data receiving nodefurther comprises a receiving unit for deriving the positions of timeintervals for receiving the selected number of transmission processesaccording to the position of the available time intervals determined bythe link control unit and according to a mapping of the number oftransmission processes configured by the transmission configuration unitonto the available time intervals in a predefined and cyclically order.A first transmission and any required retransmission of a single dataportion are mapped to a single transmission process.

According to another aspect of the present invention, a datatransmitting node is provided for communicating with a data receivingnode in a mobile communication system using a transmission protocol fordata transmission from the data transmitting node to a data receivingnode. The data transmitting node comprises: a link control unit fordetermining a position of time intervals available for data transmissionfrom the data transmitting node to the data receiving node; a receivingunit for receiving from the data receiving node an indicator indicatinga number of transmission processes to be applied for the transmission ofdata to the receiving node; a transmission configuration unit forconfiguring the number of transmission processes to the value signalledwithin the indicator; a transmitting unit for deriving the position oftime intervals for transmitting data to the data receiving nodeaccording to the position of the available time intervals and by mappingof the received number of transmission processes onto the available timeintervals in a predefined order and cyclically, wherein a firsttransmission and any required retransmission of a single data portionare mapped to a single transmission process; and judging unit forjudging whether the number of transmission processes indicated by theindicator leads to a round trip time of data transmission for atransmission process to the receiving node lower than the minimum roundtrip time supported by the mobile communication system, wherein the datato be transmitted are user data and signalling data and when the judgingunit judges positively, no transmission of user data to the receivingnode takes place in those time intervals, which cause said round triptime for a transmission process to be lower than said minimum round triptime.

According to yet another aspect of the present invention, a datatransmitting node is provided for communicating with a data transmittingnode in a mobile communication system using a retransmission protocolfor data transmission from a data transmitting node to the datareceiving node. The data transmitting node comprises a link control unitcapable of determining a position of time intervals available for datatransmission from the data transmitting node to the data receiving node,and a retransmission control unit for configuring a number oftransmission processes for transmitting data based on the positions ofthe available time intervals determined by the link control unit. Thedata transmitting node further comprises a transmitting unit forderiving the position of time intervals for transmitting data to thedata receiving node according to the position of the available timeintervals and by mapping of the number of transmission processesconfigured by the transmission configuration unit onto the availabletime intervals in a predefined and cyclically order. A firsttransmission and any required retransmission of a single data portionare mapped to a single transmission process.

Preferably, the number of transmission processes is selected so as tocontrol the round trip time of the retransmission protocol or based on amessage received from the data receiving node.

Still preferably, the data receiving node is a network node in moreparticular a base station and the data receiving node is a relay node.However, the data receiving node and the data receiving nodes may alsobe, respectively, any one of a network node, a relay node, or acommunication terminal.

According to an embodiment of the present invention the number oftransmission processes is selected according to predefined rules in thesame way at both the data receiving node and the data transmitting node(the first and the second node).

According to another embodiment of the present invention, the number oftransmission processes is determined at the data receiving node andsignalled to the data transmitting node, for instance as an indicator.

Advantageously, the indicator can take a value for indicating that thefirst node shall determine the number of transmission processesimplicitly, i.e. based on a minimum round trip time between the firstnode and the second node and based on available positions of timeintervals available for data transmission from the first (datatransmitting) node to the second node (data receiving). In particular,the indicator may take values such as integer numbers (which may befurther binarized) directly representing the number of transmissionprocesses. Another value, which can be out of the range for signallingthe number of processes may then be reserved for signalling the implicitdetermination. It may be a value such as zero or a maximum number ofprocesses allowed plus an offset (such as one), or a value that isdesignated as reserved. Such a signalling is advantageous since noseparate indicator for implicit determination is required. However, thepresent invention is not limited thereto and, in general, a separateindicator may be signalled as well. Alternatively, the implicitdetermination may be triggered by a particular setting of otherparameters.

The positions of the available time intervals may also be signalled fromthe second node to the first node. Alternatively, it may be determinedfrom another signal from the second node to the first node. For example,the second node may signal the available time intervals fortransmissions from the second node to the first node. From this, theavailable time intervals for transmission from the first node to thesecond node can be determined by applying an offset, which is preferablyan integer number of time intervals.

Preferably, the number of transmission processes is configured as thesmallest number of transmission processes leading to the round trip timeof data transmission from between the two nodes (data transmitting anddata receiving) not lower than the minimum round trip time supported bythe mobile communication system for data transmission between the twonodes.

The round trip time of one transmission process of the retransmissionprotocol is defined as the time between two consecutive transmissionopportunities for the same transmission process. The minimum round triptime is a system parameter derived based on the processing timerequirements of the communicating nodes.

According to still another embodiment of the present invention, the datatransmitting node is a relay node and the data receiving node is anetwork node and the position of time intervals available for datatransmission from the relay node to the network node is determined basedon the timing of uplink transmission processes between communicationterminal and the relay node (on relay access uplink). In particular, therelation of the relay access uplink timing to the timing of availabletime intervals on the relay uplink is taken into account.

Preferably, on the relay access uplink the transmission processes areidentified, the receiving time interval of which overlaps with any oftime intervals that can be configured as time intervals available fordata transmission on the relay uplink backhaul. The process number ofthese identified processes is determined. As time intervals availablefor data transmission then the time intervals are selected, whichoverlap with a limited number of process numbers of uplink transmissionprocesses between the relay node and a communication terminal in orderto limit the number of the uplink transmission processes being delayed.In particular, the time intervals may be selected, which overlap withthe smallest number of affected processes.

Preferably, the position of the time intervals for transmitting ofuplink grants for data transmission and/or time intervals fortransmitting of feedback information is determined based on the positionof time intervals for transmitting data from the relay node to thenetwork node.

Advantageously, the mobile communication system is a 3GPP LTE system orits enhancements, the first node is a relay node, the second node is anodeB and the indicator is transmitted within the RRC signalling relatedto backhaul subframe configuration. Further more, the time intervals maycorrespond to the subframes of the 3GPP LTE system.

According to an embodiment of the present invention, at the first node,the number of transmission processes is configured to the valuesignalled within the indicator. Still at the first node it is judgedwhether the number of transmission processes indicated by the indicatorleads to a round trip time of data transmission for a transmissionprocess from the first node to the second node being lower than theminimum round trip time supported by the mobile communication system fordata transmission from the first node to the second node, wherein thedata to be transmitted are user data and signalling data, and, when thejudging step judges positively, no transmission of user data from thefirst node to the second node takes place in those time intervals, whichcause said round trip time for a transmission process to be lower thansaid minimum round trip time.

The “no transmission” may only relate to the user data, which isadvantageous since the control information (signalling) such as feedbackinformation may still be transmitted in order to be provided as soon aspossible. Alternatively, the “no transmission” may also apply forsignalling data. The “no transmission” may refer to the fact that nouser data and/or signalling data are transmitted. Advantageously,discontinuous transmission may be used when no user data and signallingdata are transmitted; the transmitting circuitry is switched off.

Moreover, the mapping of transmission processes is performed bycyclically mapping the selected number of processes onto the availabletime intervals for transmission from the first node to the second node.After this mapping, the time intervals are determined, in which there isno transmission of user and/or signalling data. Thus, the mapping ofprocesses onto available time intervals does not specially handle thetime intervals in which no transmission is to take place. After themapping, the time intervals which, for a particular transmissionprocess, lead to a too small round trip time shall not be used for thetransmission of that particular process. Other processes or timeintervals for said process that observe the minimum round trip timeremain unaffected.

The transmission of data from the first node to the second node mayinclude transmitting acknowledgements for data received from the secondnode at the first node, transmission of the acknowledgements takingplace in time intervals located a fixed number of time intervals afterthe transmission of said data, and the acknowledgements located in thosetime intervals in which no transmission takes place may be bundled ormultiplexed with another acknowledgement sent in a different timeinterval. Bundling or multiplexing provides an efficient way to utilizeone feedback opportunity to communicate feedback data related todifferent transmission processes. This is especially advantageous whendiscontinuous transmission is employed where a transmission opportunitymay be lost.

In accordance with still another aspect of the present invention, amobile communication system is provided, comprising a network nodeapparatus according to the present invention and a relay apparatusaccording to the present invention. The system may further comprise oneor more mobile terminals capable of communicating with the relay nodeapparatus. Such a system is capable of configuring an uplinkretransmission protocol according to the present invention and oftransmitting data accordingly.

According to still another aspect of the present invention, a method isprovided for receiving data at a receiving node using a retransmissionprotocol for data transmission between two nodes in a communicationsystem. First, positions of time intervals available for datatransmission between the two nodes are determined. Based thereon, anumber of transmission processes for transmitting data from the datatransmitting node to the data receiving node is selected. The positionsof time intervals for receiving the selected number of transmissionprocesses for data transmission from the data transmitting node arederived according to the position of the available time intervals andaccording to a mapping of the selected number of transmission processesonto the available time intervals in a predefined and cyclically order.

A first transmission and any required retransmission of a single dataportion are mapped to a single transmission process.

According to yet another aspect of the present invention, a method isprovided for transmitting data from a data transmitting node using aretransmission protocol for data transmission to a data receiving nodein a mobile communication system. Positions of time intervals availablefor data transmission are determined. Accordingly, a number oftransmission processes for transmitting data from the transmitting nodeto the receiving node is selected. The positions of time intervals fortransmitting data to the network node are derived according to theposition of the available time intervals and by mapping of theconfigured number of transmission processes onto the available timeintervals in a predefined and cyclical order.

In accordance with yet another aspect of the present invention, acomputer program product is provided which comprises a computer readablemedium having a computer readable program code embodied thereon, theprogram code being adapted to carry out any embodiment of the presentinvention.

The above and other objects and features of the present invention willbecome more apparent from the following description and preferredembodiments given in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a schematic drawing illustrating 3GPP LTE architecture;

FIG. 2 is a schematic drawing illustrating 3GPP LTE architecture of theradio access network E-UTRAN;

FIG. 3 is a block diagram illustrating downlink baseband processing inLTE system;

FIG. 4 is an illustration of radio frame structure for LTE FDD system;

FIG. 5 is an illustration of radio frame structure for LTE TDD system;

FIG. 6 is an illustration of physical resources in a time-frequency gridfor uplink LTE;

FIG. 7 is a schematic illustration of timing of the uplink HARQ in 3GPPLTE;

FIG. 8 is a schematic illustration of 3GPP LTE architecture with a donorNodeB and a relay node;

FIG. 9 is a schematic illustration of the relay backhaul downlinksubframe structure in LTE-A;

FIG. 10 is a schematic illustration of an example relay backhaul uplinkHARQ timing for the case, in which Release 8 LTE uplink HARQ is appliedto the relay backhaul link in LTE-A;

FIG. 11 a schematic illustration of another relay backhaul uplink HARQtiming for the case, in which Release 8 LTE uplink HARQ is applied tothe relay backhaul link in LTE-A;

FIG. 12 a schematic illustration of relay backhaul uplink HARQ timingwith 10 ms round trip time;

FIG. 13 is a schematic drawing illustrating showing the relation betweenthe timing of the relay backhaul link with the HARQ of 10 ms round triptime and the relay access link;

FIG. 14 is a schematic drawing illustrating of the backhaul uplink HARQin accordance with the present invention;

FIG. 15A is a schematic drawing illustrating mapping of one HARQ processon relay uplink backhaul subframes for different numbers of processes;

FIG. 15B is a schematic drawing illustrating mapping of two HARQprocesses on relay uplink backhaul subframes for different numbers ofprocesses;

FIG. 15C is a schematic drawing illustrating mapping of three HARQprocesses on relay uplink backhaul subframes for different numbers ofprocesses;

FIG. 16 is a schematic drawing showing a system including a network nodeand a relay node in accordance with the present invention;

FIG. 17 is a schematic drawing illustrating an example of mappingdifferent numbers of HARQ processes on backhaul uplink assuming a firstconfiguration of Un downlink and uplink transmission;

FIG. 18 is a schematic drawing illustrating an example of mappingdifferent numbers of HARQ processes on backhaul uplink assuming a secondconfiguration of Un downlink and uplink transmission;

FIG. 19 is a schematic drawing illustrating an example of mappingdifferent numbers of HARQ processes on backhaul uplink for a thirdconfiguration of Un downlink and uplink transmission; and

FIG. 20 is a flow diagram illustrating the methods performed at the datatransmitting and data receiving node according to an embodiment of thepresent invention.

DETAILED DESCRIPTION

The present invention relates to communication in a wireless mobilesystem on the link between two nodes, in particular, to configuration ofa retransmission protocol for data transmission between the two nodes.

The problem underlying the present invention is based on the observationthat a relay node cannot transmit and receive at the same time in onefrequency band. This results in limitations of a choice of the timeintervals available for the transmission of data from the relay node tothe network node. Such limitations may lead to an increased averageround trip time, especially in case of a synchronous retransmissionprotocol applied to the backhaul uplink. However, a synchronousretransmission protocol has an advantage of implicitly derived timingleading to low signaling overhead.

The problem underlying the present invention may occur for any two nodesin a communication system and the present invention may thus be appliedto any two nodes in a communication system, not only to a network nodeand a relay node, which have been chosen only as an example. The problemwith irregular (within a certain time period such as a frame or a numberof frames) distribution of available time intervals may also occur intransmission between two network nodes, or between a network node and aterminal, or between a relay node and a terminal, etc. Furthermore, arelay node may in general also incorporate functions of a network node.

The present invention provides an efficient mechanism for transmittingdata using a retransmission protocol between a first node and a secondnode even for the case in which the available time intervals for thetransmission are irregularly distributed. The number of transmissionprocesses is selected and their mapping to time intervals available fortransmission of the uplink data is defined. In particular, the number oftransmission processes is determined based on the location of availabletime intervals. The transmission processes are mapped (HARQ processes)in a predefined order and repeated cyclically on the available timeintervals. Based on the selected number of transmission processes andbased on the resulting transmission process mapping, the time intervalsfor uplink transmission and reception of scheduling related controlsignalling (including ACK/NAK) may be determined.

The number of transmission processes may be selected also in order tocontrol the round trip time between the two nodes.

Round trip time is a time needed for a signal transmitted from a senderto arrive at the receiver and returning back. The round trip time of onetransmission process of the retransmission protocol is defined as thetime between two consecutive transmission opportunities for the sametransmission process. In synchronous retransmission protocols, theminimum round trip time is defined by the synchronous timing. Forinstance, in the retransmission protocol illustrated in FIG. 11, thevalue of minimum round trip time is 8 ms, corresponding to the timebetween the first transmission of data from relay node (RN) on PUSCH andthe feedback on PHICH/PDCCH send 4 ms later plus the fixed time of 4 msbetween this feedback information and the transmission of further data(either retransmission of the transmitted data or a first transmissionof other data). These fixed response times are typically chosen withregard to the processing capabilities of the communication nodes, forinstance, by considering the time needed for receiving, demultiplexing,demodulating, decoding and evaluating of the transmitted information aswell as the time for preparing and sending an appropriate response(possibly including coding, modulating, multiplexing, etc.). As can beseen from FIG. 11, the real round trip time even for a synchronousretransmission protocol may differ from the minimum round trip time inparticular cases. Thus, an average round trip time may be used as ameasure for delay on a link.

FIG. 15A shows subframes of a PUSCH for uplink transmission of data froma relay node to a donor eNB. Subframes with numbers 1 and 7 (numberedstarting from 0) are available for transmission of the data from therelay node to the donor eNB. The single HARQ process denoted “P1” ismapped in accordance with the present invention onto each availablesubframe, resulting in a smallest achievable round trip time 1501 offour-subframe duration, which corresponds in LTE-A to 4 ms. A longerround trip time of 6 ms also occurs in this mapping scheme.

FIG. 15B illustrates mapping of two transmission processes denoted “P1”and “P2” onto the available subframes in accordance with the presentinvention. The two processes are mapped alternately, i.e. in the fixedorder P1, P2 and cyclically. This mapping results in a smallestachievable round trip time 1502 of 8 ms corresponding to duration of 8subframes. The longer round trip time resulting from this mapping is 12ms.

FIG. 15C illustrates mapping of three transmission processes denoted“P1”, “P2”, and “P3” onto the same available subframes as in FIGS. 15Aand 15B. The three processes are mapped in a fixed order P1, P2, P3periodically onto the available subframes. This leads to a smallestachievable round trip time of 14 ms. The longer round trip timeresulting from this mapping is 16 ms.

Thus, according to the present invention a control of the round triptime in a retransmission protocol is enabled by means of configuring thenumber of transmission processes, since the mapping of the processesonto the available subframes is specified in the present invention.

Preferably, the smallest round trip time of a transmission process suchas 1501, 1502, 1503 is to be configured larger than or equal to theminimum round trip time supported by the system. In LTE-A backhauluplink, the minimum round trip time is given by the system to allowenough processing time for the d-eNB and the relay node. A synchronousuplink protocol respecting the limitations posed by the minimum roundtrip time may be supported providing thus enough time for processing inthe nodes involved in communication. In the examples shown by thefigures, the minimum round trip time is assumed to be 8 ms. As can beseen from FIG. 15A, mapping a single transmission process on theavailable subframes does not fulfil the condition that the smallestround trip time should be larger than or equal to the minimum round triptime given by the system; the smallest round trip time is 4 ms, which isless that the minimum round trip time of 8 ms supported by the system.As can be seen from FIGS. 15B and 15C, both these configurations resultin the smallest round trip time equal to (cf. 8 ms in FIG. 15, twoprocesses) or larger than (cf. 14 ms of FIG. 15C, three processes) theminimum system round trip time. Similarly, each higher number oftransmission processes (four and more) fulfils the condition.

In accordance with an embodiment of the present invention, the number oftransmission processes is selected in such a way that the resultinground trip time is as small as possible, but larger than the minimumsystem round trip time. This enables reducing the average round triptime on the relay uplink backhaul. Moreover, once the rule for mappingthe transmission processes is adopted on the relay uplink backhaul, thisrule for selecting the number of transmission processes may be followedby both d-eNB and relay node, since they both have to be aware of theconfiguration of time intervals available for the uplink transmissionfrom the relay node to the d-eNB. Such an implicit deriving of number ofprocesses at both relay node and the d-eNB has further the advantage ofno-additional overhead needed for signalling the number of processes.

Referring to FIGS. 15A, 15B, and 15C, according to this embodiment ofthe present invention, based on the available subframes number 1 and 7,the configuration shown in FIG. 15B would be selected, supporting twotransmission processes.

The processes P1, P2, and P3 denote transmission processes with anarbitrary process number. The order of transmission processes ispreferably consecutive. However, the present invention is not limitedthereto and an arbitrary ordering of the transmission processes would bepossible.

Another advantage of the present invention is the possibility tomaintain a synchronous uplink HARQ, which is efficient, since the amountof explicit signalling is minimized. In particular for the example ofLTE-A, the PUSCH transmission on each relay uplink backhaul subframe isassociated with a single uplink HARQ process identification (number).The timing relation between the PDCCH uplink grant and PUSCHtransmission on relay backhaul and corresponding feedback on PHICH/PDCCHmay be derived by the relay node and the network node (d-eNB) dependingon the configuration of the available subframes.

It is agreed in 3GPP RAN1 group that, relay uplink backhaul subframesare semi-statically configured or implicitly derived by HARQ timing fromthe downlink backhaul subframes. If uplink backhaul subframes areimplicitly derived by HARQ timing from downlink backhaul subframes, thetiming relation between the PDCCH/PHICH and PUSCH transmission isdefined in the specification (for instance, 4 ms in Release 8 LTE) or bya configurable parameter.

If the available uplink backhaul subframes are semi-staticallyconfigured (for instance, by RRC protocol at the d-eNB), the timingrelation between PDCCH/PHICH and PUSCH transmission should be derived sothat it is longer than the processing time at eNB and as small aspossible in order to reduce the delay.

The present invention may be advantageously used for example inconnection with a mobile communication system such as the LTE-Advanced(LTE-A) communication system previously described. However, the use ofthe present invention is not limited to this particular exemplarycommunication network. It may be advantageous for transmitting and/orreceiving of data signal and control signal over any standardized mobilecommunication system with relaying nodes, any evolved versions of such astandardized mobile communication, any future mobile communicationsystems to be standardized or any proprietary mobile communicationsystem.

In general, the present invention enables controlling the round triptime by means of configuring the number of transmission processes on theuplink between the relay node and the network node. Once the number ofprocesses is determined and the mapping of the transmission processesonto the available time intervals is applied, the time relation betweenthe uplink data transmission, feedback and grant for transmission may befixedly defined or derived based on the pattern of available timeintervals.

Thus, a synchronous uplink retransmission protocol may be supported andthe average round trip time is controlled by the present invention.Moreover, a full flexibility of 40 ms periodicity configuration forrelay downlink backhaul subframes can be supported.

According to another embodiment of the present invention, the number oftransmission processes is configured in the network node and explicitlysignalled to the relay node. The relay node determines the number oftransmission processes from an indicator received from the network node.This solution requires signalling of the number of processes. However,it also provides advantages. For instance, the complexity and testingeffort can be reduced at the relay node. Moreover, signalling of thenumber of transmission processes allows for a more flexible controllingthe round trip time. A longer round trip time may be supported byincreasing the number of uplink transmission processes on the uplinkbetween the relay node and the network node. A shorter round trip timemay be supported by reducing the number of uplink transmissionprocesses. Even a round trip time smaller than a minimum system roundtrip time may be selected if possible from the point of view ofimplementation of the network node and the relay node processing.

Currently, it has been agreed in 3GPP RAN1 group that relay downlinkbackhaul subframes are semi-statically configured and relay uplinkbackhaul subframes are semi-statically configured or implicitly derivedby HARQ timing from downlink backhaul subframes as described above.

Moreover, when a relay node transmits data to a network node, it cannotat the same time receive data from a mobile station. This leads tolimitations of available subframes on both access link (the link betweena relay node and a mobile terminal) and backhaul link (the link betweena relay node and a network node). As a consequence, the average roundtrip time increases and the transmission processes on the uplink betweenthe mobile terminal and the relay node may lose their chance fortransmission. This results in delay of the affected processes and thus,in an overall performance degradation.

All retransmission mechanisms discussed above have such an impact on theuplink between the mobile terminal and the relay node.

FIG. 13 illustrates this problem based on the example of the 10 ms-RTTsolution for LTE-A described above with reference to FIG. 12. Atime-division based relay node cannot transmit and receive at the sametime in one frequency band. When such a relay transmits to the d-eNB, itcannot receive at the same time from the attached r-UEs. Consequently,the associated uplink HARQ processes in r-UEs lose their chance fortransmission. FIG. 13 shows both, the relay backhaul link 1310 similarto the relay backhaul link of FIG. 12 and the relay access link 1320with eight HARQ processes configured. An arrow 1340 points to theimpacted HARQ processes, where the r-UE cannot transmit to the relaynode since the relay node transmits to the d-eNB. According to the 10ms-RTT solution, always a different uplink HARQ process number in ther-UEs is impacted. As can be seen in FIG. 13, at least the half (four)of the uplink HARQ processes 1350 are impacted and suffer from a longerdelay of 16 ms since with eight configured processes the next chance totransmission is 8 ms later. When four or more than four subframes areconfigured per 10 ms on relay uplink backhaul, all eight uplink HARQprocesses in r-UEs are delayed. In such a case, it is impossible for therelay node to smartly schedule delay critical data on a non-delayeduplink HARQ process in r-UEs.

In order to overcome this problem, in accordance with still anotherembodiment of the present invention, the timing of the uplinktransmission processes between the mobile station (r-UE) and the relaynode is taken into account when configuring the available time intervals(subframes) for the uplink transmission between the relay node and thenetwork node. The general idea is to configure the available uplinkbackhaul time intervals in such a way that a smaller number of uplinkretransmission (HARQ) processes on the uplink between a mobile terminaland the relay node are delayed.

FIG. 14 illustrates such a mechanism. Transmission process P1 on thebackhaul uplink is mapped to the available time intervals on PUSCH insuch a way that only two transmission processes on the uplink accesslink are affected, namely the transmission processes 1450 with processnumber 3 and 7. Thus, only limited transmission processes on the uplinkbetween the mobile terminal and the relay node will have a longer delay.So the relay node may, for instance, schedule delay critical data onthose non-delayed transmission processes and schedule delay non-criticaldata on those delayed transmission processes.

Thus, according to this embodiment of the present invention, theconfiguration of the time intervals for transmitting the data from therelay node to the network node may be performed so as to affect smallernumber of processes on the access link. In order to facilitate such aconfiguration, the network node may first determine the process numberof the access transmission processes (between the mobile terminal andthe relay node) to be overlapped with time intervals for transmission ofdata in uplink from the relay node to the network node. Based thereon,time intervals are selected available for transmission in the relaybackhaul uplink that overlap with a lowest possible number of processnumbers of the transmission processes on the access link. In general,the available time intervals selected does not need to lead to a lowestpossible number of process numbers affected on the access link. Themechanism of this embodiment may also be used just for lowering thenumber of affected processes on the access or for ensuring that certainprocess numbers are not delayed.

The main advantage of the present embodiment is the resulting lowerimpact of the backhaul transmission (transmission between the relay nodeand the network node) on the access transmission (transmission betweenthe mobile terminal and the relay node). This mechanism may be employedin addition to the present invention related to configuring the numberof transmission processes and their mapping on the available timeintervals. However, such a mechanism may also be applied to any othersystem allowing for configuration of available time intervals fortransmission of data between a relay node and a network node.

The present invention has been described based on examples of aretransmission protocol for 3GPP LTE-A system. Two downlink signallingchannels associated with the uplink data transmission on the backhaullink between a network node and a relay node have been described: PHICHand PDCCH. However, the proposed backhaul uplink HARQ protocol canoperate without PHICH. In order to facilitate this, PDCCH is used toindicate positive or negative acknowledgements (ACK/NAK) for theconfigured HARQ processes.

In more detail, the LTE HARQ mechanism employs a PDCCH at an expectedfeedback time for a given transmission process (or a given data unit) totrigger either a transmission of a new data unit or the retransmissionof an old data unit by means of the PDCCH content. In absence of a PDCCHat an expected feedback time for a given transmission process (or agiven data unit), the PHICH at that same time is responsible to give ashort efficient feedback that either triggers a retransmission of an olddata unit (usually associated with PHICH=NACK) or that triggers asuspension mode in which the data transmitter is waiting for an explicitnew command by PDCCH at a later point of time (usually associated withPHICH=ACK). In case the mechanism is changed such that there is no PHICHor equivalent feedback signal existing in the protocol, the followingembodiment can be beneficially employed. As before, a PDCCH at anexpected feedback time for a given transmission process (or a given dataunit) is triggering either a transmission of a new data unit or theretransmission of an old data unit by means of the PDCCH content. Theabsence of a PDCCH at an expected feedback time for a given transmissionprocess (or a given data unit) triggers a suspension mode in which thedata transmitter is waiting for an explicit new command by PDCCH at alater point of time.

In case that it is desirable to implement the mechanism without PHICHsignals into a protocol or entity that expects the existence of PHICH,in a further embodiment the absence of a PDCCH at an expected feedbacktime for a given transmission process (or a given data unit) istriggering the same behaviour as the reception of a PHICH=ACK signal atthat same time. In other words, the detection of PHICH=ACK is simulated.

Furthermore, more uplink backhaul subframes may be configured than thenumber of configured downlink backhaul subframes. In such a case, anuplink grant (on PDCCH or PHICH) in one downlink backhaul subframecorresponds to an uplink (PUSCH) transmission in several uplink backhaulsubframes. In order to uniquely determine the timing of the grant(PDCCH), the data transmission (PUSCH) and/or the feedback (PHICH) inthe scheme of the present invention, an index of the correspondinguplink backhaul subframe may be indicated in the uplink grant.Alternatively, the uplink transmission process identification may beindicated in the uplink grant. The uplink transmission processidentification would uniquely identify the process number of the relateduplink transmission process. Since one uplink transmission processidentification is associated with one uplink backhaul subframe withinone round trip time, this signalling enables for clear establishing ofthe retransmission protocol timing in the uplink backhaul.

The above described mechanisms have been designed so as to maintain thebackward compatibility of the user terminals. Thus, a mobile terminalcommunicates with a relay node in the same way as with a network node.However, in accordance with yet another embodiment of the presentinvention, the later mobile terminals (for instance UEs compliant with3GPP LTE-A Release 10 and more) may be capable of distinguishing betweenrelay nodes and network nodes.

In particular, the configured uplink backhaul subframes available forthe transmission may be signaled to the release-10 r-UEs. In theseconfigured uplink backhaul subframes, the release-10 r-UEs would assumethat no signal will be received from the relay node since the relay nodetransmits to the network node (d-eNB). Accordingly, a Release-10 mobileterminal shall assume reception of a positive acknowledgement (ACK) forthe corresponding uplink transmission process on the relay access link(between the mobile terminal and the relay node). As a consequence ofthe positive acknowledgement, the corresponding uplink transmissionprocess on relay access link is suspended. Such a protocol has anadvantage that the mobile terminal does not need to try to decode theassociated PHICH, which enables saving the energy in such an r-UEs.Moreover, a PHICH error is avoided.

FIG. 16 illustrates a system 1600 according to the present invention,comprising a network node 1610 as described above in any of theembodiments and a relay node 1650 as described above in any of theembodiments. The network node 1610 is a node such as a base station, anode B, an enhanced node B, etc., to be connected to a network and to arelay node 1650. The relay node 1650 is connectable to the network node1610 preferably via a wireless interface 1620. However, the relay node1650 may also be connected to the network node via a cable connection.The relay node 1650 is further connectable to at least one mobileterminal 1690 via a wireless interface 1660. The relay node 1650 may bean apparatus similar to the network node 1610. However, the relay node1650 may also differ from the network node. In particular, the relaynode may be simpler and may support less functions than the network node1610. The advantage of providing between a network node 1610 and themobile terminal 1690 a relay node is for instance, increasing thecoverage, enhancing the group mobility, etc. For a user terminal 1690the relay node 1650 may seem as a normal network node 1610. This isbeneficial especially in view of the backward compatibility of olderuser terminals. However, the mobile terminal 1690 may also be capable ofrecognizing between a relay node and between a network node. The mobileterminal 1690 may be a mobile telephone, a PDA, a portable PC, or anyother apparatus capable of mobile and wireless connection to a networknode and/or a relay node.

A network node in accordance with the present invention includes a linkcontrol unit for selecting time intervals to be available for the uplinktransmission 1620 of data from the relay node 1650 to the network node1610. The selection of the available time intervals may be performedaccording to the above embodiments, for instance based on theconfiguration of downlink time intervals on the relay link. Furthermore,access link timing may be considered for configuration of the availabletime intervals. In particular, the timing of the transmission processeson the uplink 1660 between the mobile terminal 1690 and the relay node1650. Other ways of selecting the available time intervals are alsopossible.

In the system 1600, depending on the method for selecting the availabletime intervals, the selection may be performed by the link control unit1611 and 1651 in the same way at the network node 1610 and at the relaynode 1650. This is possible, if the way for determining of the timeintervals is unique, such as in the case where it is determined based onthe downlink time intervals and the exact rules are defined, or in thecase of avoiding the time delay on the access uplink 1660. However, thenetwork node 1610 may also select the available time intervals andsignal them (schematically illustrated by an arrow 1640) to the relaynode 1650. The relay node receives the signal 1640 and configures in itslink control unit 1651 the available time intervals accordingly. Thesignalling may be semi-static, as proposed, for instance, in the LTEsystem. However, the signalling could also be dynamic.

Once the available time intervals are determined, according to thepresent invention, a number of transmission processes for transmission1620 of data on relay link is selected. This may be performed by thetransmission configuration unit 1612, 1652 of both the network node 1610and the relay node 1650 in the same way, in case unambiguous rules aredefined. Alternatively, the link control unit 1611 of the network nodedetermines the number of transmission processes on the relay link andsignals it (schematically illustrated as an arrow 1630) to the relaynode 1650. The link control unit 1652 of the relay node 1650 receivesthe number of transmission processes from the network node and employsit for mapping of the data to be transmitted onto the available timeintervals. The mapping is performed by the transmission unit 1653 in therelay node according to a predefined order and cyclically. Thus, themapping is unique once the number of processes is known. Since thenetwork node 1610 has also knowledge of the number of processes and theavailable time intervals, its receiving unit 1613 may derive the mappingof the processes onto the available time intervals in the same way asthe transmitting unit 1653 of the relay node 1650. Based on thismapping, both the network node 1610 and the relay node 1650 configuretheir timing of the retransmission protocol. After the configuration,the transmission 1620 of data from the relay node to the network nodemay take place.

In addition, based on the determined timing, the timing of receiving andtransmitting uplink grants and acknowledgement feedback may also bederived according to a fixed rule in both the network node and the relaynode.

In the above description of the nodes and the system according to thepresent invention, an example of relay node and a network node has beentaken. However, the two communication nodes 1610 and 1650 are notnecessarily the network node and relay node, respectively. The nodes1610 and 1650 may be any nodes included in a communication systemcommunication together using a retransmission protocol of the presentinvention.

The present invention thus introduces an efficient retransmissionprotocol (HARQ protocol) for backhaul uplink. This protocol issynchronous with respect to the order of transmitting the transmissionprocesses since the mapping of the transmission processes to availableuplink subframes is performed in consecutive order and cyclically. Thepresent invention also provides two possibilities for determining thenumber of backhaul uplink transmission processes. The number oftransmission processes on backhaul uplink can be minimized as animplicit function of the uplink backhaul subframe configuration, whichmay be itself an implicit function of the downlink backhaul subframeconfiguration. This means that at the network node as well as at therelay node, the number of transmission processes is determinedimplicitly in the same way based on the configuration of the uplinkbackhaul and, in particular, based on the available uplink backhaulsubframes. Alternatively, the number of transmission processes can besignaled explicitly, for instance, from the network node to the relaynode. Advantageously, the number of transmission processes is signaledwithin the RRC signalling as a relay node specific signal.

The implicit determination of the number of backhaul uplink transmissionprocesses leads to an optimum number of transmission processes from thepoint of view of delay minimizing and buffering requirements. Moreover,no explicit signalling is necessary, leading thus to a bandwidthefficient solution. However, there is no flexibility in configuration.

On the other hand, explicit signalling of the number of transmissionprocesses from network node to the relay node enables, in general, thefull control by the network node with respect to the number oftransmission processes and provides more flexibility by setting thenumber of transmission processes higher than the implicitly derivedminimum. Setting the number of transmission processes higher than theminimum may lead to a more time-regular or even fixedprocess-to-subframe pattern. For instance, the same RTT for alltransmission processes may be achievable or a smaller RTT variationwithin a single transmission process may be possible, etc.

It may be particularly advantageous to include a parameter forsignalling the number of transmission processes together with signallingfor the backhaul subframe configuration. For instance, in case of theLTE system, the number of transmission processes may then be signaled byRRC signalling within the signalling related to the backhaul subframeconfiguration. Accordingly, in case of modified backhaul subframeconfiguration, no additional signalling for the number of transmissionprocesses is required and thus, the possibility of violating the minimumRTT requirement may be reduced.

The explicit signalling parameter may indicate, for instance, an integervalue from 1 to k, k being the maximum configurable number oftransmission processes. For LTE Release 8 FDD, the value of k is 8. Inaddition, the parameter may also take a value which is interpreted asindication that the number of transmission processes is to be determinedimplicitly as described above. For instance, apart of the valid set ofnumber of transmission processes {1, 2, 3, . . . , k} a value “0” or avalue “k+1” or any other reserved value may indicate that the number oftransmission processes is to be determined implicitly. Although for theLTE Release 8 k=8 is defined, k=6 could also be sufficient if therelation to the MBSFN subframes is considered as described above forrelay node sharing the same frequency spectrum for the access link andthe backhaul link. In such a case, a parameter with 8 possible valuesmay be signaled with the mapping of parameter values on the number oftransmission processes as follows: parameter values 1 to 6 would map onthe corresponding number of transmission processes 1 to 6. At least oneof the remaining values may be used to signal that the implicit methodshall be used to determine the number of transmission processes. Theadvantage of keeping the number of possible parameter values to notexceed 8 is that in order to signal 8 values, a 3-bit indicator isnecessary. Extending to 9 or more values requires one signalling bitmore. However, this was only an example and any other mapping may alsobe applied for signalling the number of transmission processes accordingto this embodiment.

Alternatively, the explicit signalling allows any number of transmissionprocesses, i.e. any value from the set of values {1, 2, 3, . . . , k};however, the number of transmission processes is provided only as anoptional configuration parameter. If the parameter is present in theconfiguration signal, then the signaled value is applied. If theparameter is not present, then the minimum number of requiredtransmission processes is determined implicitly and applied.

On the other hand, in general, the explicit signalling enables to signalalso a configuration in which the requirement on delay between adjacentsubframes allocated for the same process is less than the minimum RTT.It may be noted that in a LTE Release 8 FDD system, the minimum RTT forthe same process is defined as 8 ms. In order to provide moreflexibility and at the same time overcome the above problem of theexplicit signalling, the behavior of the relay node may be specifiedaccording to one of the following mechanisms which represent variousembodiments of the present invention.

The first possibility is that the signaled value leading to a delaysmaller than the minimum RTT is ignored and the implicit determinationis used for obtaining a valid number of transmission processes, i.e., asmallest possible number of transmission processes leading to a distancebetween two backhaul uplink transmissions for a single process of atleast minimum RTT for each process. When the signaled value does notlead to delay between two transmissions of the same process smaller thanminimum RTT, it is adopted. This solution provides flexibility and, atthe same time, avoids problems with missed (re)transmissionsopportunities.

Another possible behavior of the relay node is to ignore any signaledvalue of number of transmission processes which would result, for thegiven configuration of backhaul uplink subframes or time intervals, to adistance smaller than the minimum RTT between two backhaul uplinktransmissions of the same process, and consequently not execute anytransmissions until a number of transmission processes is obtained thatfulfils the minimum RTT between two backhaul uplink transmission for allprocesses, for example by mean of a reconfiguration of the number oftransmission processes by explicit signalling. Alternatively, a defaultvalue of the maximum number of processes k can be applied to be able tocontinue with a rudimentary data delivery.

However, ignoring the signaled value or changing it distributes thecontrol of the number of transmission processes to both the network nodeand the relay node. In order to avoid such a situation, another possiblebehavior of the relay node is to apply the signaled number oftransmission processes even in case it does not fulfill the requirementon minimum RTT for all involved processes, and to use occasional DTX(discontinuous transmission). DTX should be applied in thosetransmission time intervals or subframes where the minimum RTTrequirement is not fulfilled; some examples are given hereafter. DuringDTX, at least part of the transmitter circuitry can be switched off.This has advantages such as reduction of the power consumption andinterference generation in the system. In particular, in case thesignaled number of transmission processes violates the minimum RTT, therelay node transmits only in subframes which fulfill the minimum RTTrequirement for a transmission process. In other subframes (referred toas “violating subframes” later in this document since they violate theminimum RTT requirement) no data transmission is performed, even if therelay node had received a valid grant for uplink resources in thosesubframes. Such behavior leads to a so-called “heavy downlink” meaningthat there are more downlink shared channel opportunities fortransmission than the uplink opportunities (subframes).

The discontinuous transmission may be applied only to transmission ofdata, whereas the control information such as transmissionacknowledgements for downlink data transmission(s) (positive and/ornegative) may still be transmitted in the violating subframes. Forexample, in 3GPP LTE, the transmission on PUSCH would be switched offfor the violating subframes. However, the transmissions of ACK/NACKmessages on PUCCH for earlier PDSCH transmission(s) could still beallowed. In such a case, the relay node can transmit the feedback fordownlink transmissions as soon as possible, leading to a reduced latencyof the downlink data transmission.

Alternatively, the DTX may be applied to any or all uplink physicalchannels in a violating time interval, e.g. there is no transmission ofdata and no transmission of control signalling on the backhaul uplinksubframe. For LTE this would mean that there is no transmission onPRACH, PUSCH and PUCCH.

DTX of the backhaul uplink subframes may lead to missed opportunitiesfor sending the feedback, particularly if the DTX operation applies tophysical or logical control channels, and thus would lead to anuncertainty at the network side as to whether a downlink transmissionhas been successfully decoded or not. In order to overcome this problem,ACK/NACK signalling information for the backhaul uplink may beadvantageously bundled or multiplexed in the next available backhaul ULPUCCH transmission, or, in general in the next available controlinformation transmission opportunity. The bundling or multiplexing ofacknowledgements may work similarly as, for instance, in the LTE Release8 TDD (cf., for instance, specification 3GPP TS 36.213, “EvolvedUniversal Terrestrial Radio Access (E-UTRA); Physical layer procedures”,Section 7.3, which is incorporated herein by reference). From theacknowledgement bundling or multiplexing operation perspective, the DTXsubframe would be handled like a downlink subframe, as there iseffectively no uplink transmission opportunity in a DTX subframe—justlike in a downlink subframe. In context of the above referenced methodfrom 3GPP TS 36.213, a DTX subframe would be equivalent to a subframewith PDSCH transmission. In such a case, the entire subframe that isDTX′ed on the backhaul may be used as an access uplink subframe, meaningthat it may be used for the transmission of data to the relay node froma mobile terminal.

The backhaul uplink DTX mode may be configurable by the network node forindicating whether there is no transmission only on data channel(s) (forinstance PUSCH) or in the entire uplink subframe regardless of data orsignalling information are carried thereby. The backhaul uplink DTX modemay be signaled, for instance, within the higher layer signalling.

Alternatively, the DTX mode may be defined by the relay nodecapabilities or signaled from the relay node to the network node.However, alternatively, a standard may also fixedly define any singleone of the above modes.

FIG. 17 illustrates an example of mapping one, two, and threetransmission processes on backhaul uplink (cf. rows with “HARQ process”for N=1, N=2 and N=3). In this example, subframes with numbers 3 and 7Within each radio frame are configured (available) for backhaul downlink(Un DL) transmission. This corresponds to subframes with number 3, 7,13, 17, 23, 27, etc. An assumption is made that backhaul uplink (Un UL)subframes are always available four subframes after the correspondingdownlink subframes. Then, backhaul uplink subframes are configured asnumber 1 and 7 of each radio frame, which means that the availablesubframes are subframes with number 1, 7, 11, 17, 21, 27, etc. As can beseen from FIG. 17, the minimum number of retransmission (HARQ) processesthat always fulfils a requirement of at least 8 ms long RTT for eachbackhaul uplink HARQ process is N=2, where the resulting RTT is alwaysequal to 10 ms for the N=2 processes. In case the number of transmissionprocesses N=1 is configured, every second backhaul uplink subframe isDTX (cf. horizontally dashed rectangles with number 1 meaning the firsttransmission process; delay shorter than the required minimum RTTbetween two subframes is illustrated by a dashed line; the delay equalor larger than the required minimum RTT is illustrated by a solid line).Effectively, only one single HARQ process with a 10 ms periodicity(corresponding to 10 ms RTT) is used. In particular, the uplinktransmission takes place in subframes number 7, 17, 27, etc. There is noHARQ related transmission in subframes 11, 21, 31, etc., these subframesare DTX. In contrast, the configuration of number of transmissionprocesses N=2 leads to a fixed delay of 10 ms for each of the twotransmission processes. In case of N=3, each of the three transmissionprocesses will have an repeatedly alternating delay of 14 ms and 16 ms.It may be noted that in this figure, the mapping of HARQ processesstarts on subframe 7 with process number 1 due to the assumedconfiguration being applied starting at subframe 0 in radio frame 0.Therefore, the first usable downlink subframe is subframe 3, and thefirst usable uplink subframe is subframe 7. In other radio frames 4nwhere n is an integer and n>0, subframe 1 can be used as uplink subframecorresponding to downlink subframe 7 in radio frame 4n−1. This is showne.g. by the relation between subframe 37 for Un DL and subframe 41 forUn UL in FIGS. 17-19. It should be noted that the numbering of DLsubframes in FIG. 17 cyclically from 0 to 9 is only exemplary toemphasize the structure of frames and subframes. The numbering may alsobe continuous as shown in FIGS. 18 and 19.

FIG. 18 illustrates another example of mapping one, two, and threetransmission processes on backhaul uplink. In this example, subframeswith number 3, 7, 11, 13, 17, 23, 27, 31, 33, 37 in the shown fourconsecutive radio frames are configured for Un DL transmission. Anassumption is made again that the backhaul uplink subframes are alwaysavailable after four subframes after the backhaul downlink subframes.Thus, the Un UL subframes with number 7, 11, 15, 17, 21, 27, 31, 35, 37,41, 47, etc. are configured for transmission (shown as verticallyhatched subframes). As can be seen from FIG. 18, the minimum number ofHARQ processes that always fulfils the requirement of at least 8 ms RTTfor each UL transmission process is N=3. In case the number oftransmission processes N=1 is configured; several backhaul uplinksubframes are not used for the transmission (DTX). Effectively, only asingle HARQ process with periodicity of alternating 8 ms and 12 ms delayis used. This corresponds to the average RTT of 10 ms. In particular,subframes with number 7, 15, 27, 35, 47, etc. are used for the uplinktransmission. In case N=2 is configured, to some backhaul uplinksubframes DTX has to be applied. Effectively, two HARQ process withperiodicity of alternating 8 ms, 16 ms and 16 ms are used. This resultsin average RTT of 40/3 ms. In particular, subframes with number 7, 15,27, 35, 47, etc. are used for the backhaul uplink transmission. This issimilar to re-using the 8 ms and 16 ms pattern of Release 8 (cf. FIG.11) by defining fewer HARQ processes than required to achieve theminimum RTT for the signalled number of processes, i.e. equal to orlarger than 8 ms RTT.

In one embodiment, the relation between uplink subframes and HARQprocess is not affected by the DTX behaviour. For example, process 2 isassociated to subframe 17, even though it is DTX (cf. example of FIG. 18for N=2). Likewise, due to the cyclic fashion of associating HARQprocesses to UL subframes, process 1 is associated to subframe 21 eventhough it is DTX. However, if due to another example not subframe 21 but25 is available, then process 1 is associated to subframe 25 because theprevious subframe 17 was associated to process 2. In this way, subframe25 and therefore process 1 in that subframe is not DTXed, because thetime between subframe 25 and the previous transmission opportunity insubframe 15 is not violating the minimum RTT requirement of 8 ms. On theother hand, since then the interval between subframe 25 and 31 is lessthan the minimum RTT requirement, subframe 31 is to be DTX′ed. In suchan embodiment, in order to determine a round trip time for atransmission process, subframes that are designated as DTX are not takeninto account. As an example, according to FIG. 18, the RTT between theprocess 1 transmission in subframe 31 and the previous transmission,subframe 21 is not regarded (considered) since it is designated as DTX;the previous transmission thus occurred in subframe 15, resulting in anRTT of 16 ms. In other words, in this embodiment, when it is judged thatmapping a certain process (for instance a process with number x) toavailable time intervals leads to a smaller RTT between a first and asecond time interval, wherein the second time interval is the nextavailable time interval for the same process as in the first timeinterval, than the minimum RTT, no transmission of user and/orsignalling data belonging to any transmission process takes place insuch a second time interval, without affecting the association betweentime interval and transmission process. This is because the transmissionof processes with different number follows a cyclical scheme resultingfrom mapping them onto available time intervals without considering theminimum RTT at first. Thus, the “no transmission” intervals aredetermined based on already cyclically mapped processes.

In another embodiment not shown in the figures, the cyclic mapping ofHARQ processes to subframes is ignoring the subframes designated as DTX.Therefore assuming an UL subframe configuration as shown in FIG. 18 andthe example for N=2, subframe 17 would be designated as DTX (as shown).However, the next available subframe 21 would be associated to process 2(as the previous non-DTX subframe association of subframe 15 was toprocess 1), and it would fulfil the minimum RTT requirement for process2, as the previous association for process 2 was in subframe 11,resulting in an RTT of 10 ms in this case. The effect on other subframesfollows this logic mutatis mutandis. In other words, in this embodiment,when it is judged that mapping a certain process (for instance a processwith number x) to available time intervals leads to a smaller RTTbetween a first and a second time interval, wherein the second timeinterval is the next available time interval for the same process as inthe first time interval, than the minimum RTT, no transmission of userand/or signalling data belonging to that particular transmission processx takes place in such a second time interval. As a consequence, theassociation of the process x to such a second time interval is removed,and instead the subsequent available time intervals are re-associated ina cyclical fashion as before, however starting with process x associatedto the next available time interval after said second time interval.This association needs to be judged again for compliance with theminimum RTT according to this embodiment. Thus, the “no transmission”intervals are determined during the cyclical mapping.

FIG. 19 illustrates another example of mapping one, two, and threetransmission processes on backhaul uplink. In the previous exampledescribed with reference to FIG. 18, subframes with number 3, 7, 11, 13,17, 23, 27, 31, 33, 37 in consecutive four radio frames are configuredfor Un DL transmission. In contrast, in this example, the subframes 3,7, 11, 23, 27, 31 in consecutive four radio frames are configured for UnDL transmission, i.e. subframes 13, 17, 33, 37 are no longer available.This affects the availability of the uplink subframes accordingly.However, assuming that two transmission processes are used, exactly thesame mapping of transmission processes as in the previous example can beachieved with the same number of HARQ processes and RTT (cf. alternatingRTT of 8 ms and 12 ms). In this way there are fewer subframes availablefor backhaul downlink than in the previous example of FIG. 18. Thus,with configuring fewer HARQ processes than required for fulfilling theminimum RTT requirements for all HARQ processes and assuming DTXbehaviour, it is possible to have more subframes for the backhaul DLavailable without affecting the backhaul uplink retransmission protocolor behaviour. However it may be noted that in this example, due to thedifferent subframe configuration, configuring N=2 results in this casein the same behaviour as if the number of HARQ processes is determinedfrom the implicit rule according to this invention; therefore no specialDTX mechanism needs to be employed. It can also be noted that setting inthis example N=3 results in a regular 20 ms RTT pattern for the HARQprocesses, as described previously in this document to provide anexample of a possible motivation for using more HARQ processes thanrequired to fulfil the minimum RTT criterion.

FIG. 20 summarizes an advantageous embodiment of the present invention.In particular, the methods performed are shown for two nodes—a firstnode (denoted “UL data transmitting node” in FIG. 20) and a second node(“UL data receiving node” in FIG. 20). These nodes may correspond to arelay station and a base station, respectively. However, the presentinvention is not limited thereto and other nodes may be configuredaccordingly.

In this embodiment, the second node first determines the time intervalsavailable for the transmission of data to the first node 2010 and/orfrom the first node to the second node. Then, the second node determines2010 a number of transmission processes which are to be used fortransmission of data between the first and the second node. Thedetermined number of transmission processes is signalled (2030) to thefirst node. The signalling is performed by transmitting within asignalling data to the first node an indicator which indicates aparticular number of transmission processes to be configured. Theindicator may also indicate that the number of transmission processes isto be determined implicitly based on other signalled parameters, inparticular, based on the configuration of the transmission intervalsavailable for data transmission. The signalling data may also furtherinclude the positions of time intervals available for transmissiondetermined in step 2010. The first node receives 2035 the indicator, and2040 and 2045 the number of transmission processes accordingly at thesecond node and the first node are configured, respectively. Thetransmission processes are to be mapped to the available time intervalscyclically. The first node evaluates (judges) whether such mappingresults in violating the requirement of a minimum RTT for any of thetransmission processes. In other words, it is checked 2050 if there aretime intervals for any of the transmission processes that are located ina distance smaller than the minimum RTT given by the system. If this isthe case, then no transmission 2060 of data takes place in such timeintervals. This is performed for instance by means of discontinuoustransmission (=DTX) in which the transmitter may be switched off, savingthe power and reducing the interference. The “no transmission” may applyeither to only a user data or to both user and signalling data. Forinstance, signalling data may be acknowledgements (positive ornegative), requests for grants, channel quality feedback, or generallyany signal that needs to be transmitted via a physical channel. In orderto ensure transmitting the signalling data without longer delays, thefeedback information (such as acknowledgements) may be bundled ormultiplexed with other signalling data in the other available timeintervals. The (remaining) data that is not DTXed is then transmitted2070 from the first node to the second node. The second node receivesthe data 2080 including any of user or signalling data. It should benoted that FIG. 20 is a schematic drawing only and does not present thereal timing conditions. For instance, transmitting data 2070 includestransmitting of any of the signalling or used data in a plurality ofavailable time intervals, wherein in some interval no data transmissionat all or no signalling data transmission takes place.

The description of LTE specific procedures is intended to betterunderstand the LTE specific exemplary embodiments described herein andshould not be understood as limiting the invention to the describedspecific implementations of processes and functions in the mobilecommunication network. Similarly, the use of LTE specific terminology isintended to facilitate the description of the key ideas and aspects ofthe invention but should not be understood as to limit the invention toLTE systems.

Another embodiment of the invention relates to the implementation of theabove described various embodiments using hardware and software. It isrecognized that the various embodiments of the invention may beimplemented or performed using computing devices (processors). Acomputing device or processor may for example be general-purposeprocessors, digital signal processors (DSP), application specificintegrated circuits (ASIC), field programmable gate arrays (FPGA) orother programmable logic devices, etc. The various embodiments of theinvention may also be performed or embodied by a combination of thesedevices.

Further, the various embodiments of the invention may also beimplemented by means of software modules, which are executed by aprocessor or directly in hardware. Also a combination of softwaremodules and a hardware implementation may be possible. The softwaremodules may be stored on any kind of computer readable storage media,for example RAM, EPROM, EEPROM, flash memory, registers, hard disks,CD-ROM, DVD, etc.

Most of the examples have been outlined in relation to a 3GPP-basedcommunication system, in particular LTE, and the terminology mainlyrelates to the 3GPP terminology. However, the terminology and thedescription of the various embodiments with respect to 3GPP-basedarchitectures are not intended to limit the principles and ideas of theinventions to such systems.

Also the detailed explanations of the resource mapping in the LTE areintended to better understand the mostly 3GPP specific exemplaryembodiments described herein and should not be understood as limitingthe invention to the described specific implementations of processes andfunctions in the mobile communication network. Nevertheless, theimprovements proposed herein may be readily applied in the architecturesdescribed. Furthermore the concept of the invention may be also readilyused in the LTE RAN (Radio Access Network) currently discussed by the3GPP.

Summarizing, the present invention relates to configuration ofretransmission protocol on the uplink between a network node and a relaynode. In particular, a mapping of a specified number of uplinktransmission processes is performed in a predefined order andperiodically repeated. The number of transmission processes is selectedbased on the time intervals available for the data transmission and maybe specified so as to control the round trip time on the relay uplink.The timing of the retransmission protocol may be derived accordinglyusing a predetermined rule.

The invention claimed is:
 1. A retransmission method comprising:receiving, from a relay node, a frame including a plurality of subframeson which a plurality of HARQ processes are mapped, a HARQ process of theplurality of HARQ processes being a processing unit of Hybrid AutomaticRepeat Request (HARQ), and the received frame being configured at therelay node by specifying, in a frame for communication, a plurality ofsubframes available for uplink data transmission from the relay node toa network node, selecting a number of HARQ processes based on thespecified plurality of subframes for uplink transmission, and mappingthe selected number of HARQ processes sequentially onto the specifiedplurality of subframes, wherein the number of HARQ processes isdetermined based on a parameter which is transmitted from the networknode in a backhaul subframe configuration; and retransmitting data tothe relay node according to the HARQ.
 2. The retransmission methodaccording to claim 1, wherein the selection of the number of HARQprocesses is performed such that a smallest number is selected fromamong numbers of HARQ processes where a roundtrip time is larger than aminimum system round trip time, the roundtrip time being a transmissiontime interval of a same HARQ process.
 3. retransmission method accordingto claim 1, wherein a backhaul uplink subframe corresponding to abackhaul downlink subframe is allocated to a position which is foursubframes after the backhaul downlink subframe.
 4. The retransmissionmethod according to claim 1, wherein the HARQ is an uplink repeatrequest from the relay node to the network node.
 5. A retransmissionapparatus comprising: receiving section configured to receive, from arelay node, a frame including a plurality of subframes on which aplurality of HARQ processes are mapped, a HARQ process of the pluralityof HARQ processes being a processing unit of Hybrid Automatic RepeatRequest (HARQ), and the received frame being configured at the relaynode by specifying, in a frame for communication, a plurality ofsubframes available for uplink data transmission from the relay node toa network node, selecting a number of HARQ processes based on thespecified plurality of subframes for uplink transmission, and mappingthe selected number of HARQ processes sequentially onto the specifiedplurality of subframes, wherein the number of HARQ processes isdetermined based on a parameter which is transmitted from the networknode in a backhaul subframe configuration; and transmitting sectionconfigured to retransmit data to the relay node according to the HARQ.6. The retransmission apparatus according to claim 5, wherein theselection of the number of HARQ processes is performed such that asmallest number is selected from among numbers of HARQ processes where aroundtrip time is larger than a minimum system round trip time, theroundtrip time being a transmission time interval of a same HARQprocess.
 7. The retransmission apparatus according to claim 5, wherein abackhaul uplink subframe corresponding to a backhaul downlink subframeis allocated to a position which is four subframes after the backhauldownlink subframe.
 8. The retransmission apparatus according to claim 5,wherein the HARQ is an uplink repeat request from the relay node to thenetwork node.